1. Field of the Invention
The present invention relates to a semiconductor wafer, a method of-manufacturing a semiconductor device having a ROM (read only memory), and an IC card. More specifically, the present invention relates to a test terminal (referred to as a test pad, hereinafter) used to test the ROM of the semiconductor device formed on the semiconductor water.
2. Description of the Background Art
Conventionally, a semiconductor wafer (e.g., silicon wafer) is separated into a plurality of chips, after having been cut off along scribe lines (or scribe regions). Further, the obtained chips are manufactured as various semiconductor devices, after each chip has been processed (e.g., package process) appropriately. In this manufacturing process, it is usual to execute some tests (e.g., die sorting test, product test, etc.) for the semiconductor wafer, before the chips are processed as device products.
FIG. 9 is a partial plane view showing a conventional semiconductor wafer. On a semiconductor wafer 1, there are arranged a plurality of product regions 2 each separated into a chip in the last step. Further, a plurality of scribe regions 3 are formed between two of these product regions 2, respectively. Further, an internal circuit composed of integrated circuits such as ROM, transistors, etc. is formed at each product region 2. Further a plurality of aluminum pads 41 to 43 are formed so as to be connected to an external circuit electrically. On the other hand, these pads 4 are electrically connected to the internal circuit, and arranged at a peripheral portion, for instance at the product region 2, respectively. In addition, a test pad 40 is also arranged together with these input and output pads 41, 42 and 43, respectively.
In the IC test of the conventional semiconductor device, these test pads 40 to 43 as shown in FIG. 9 are used. Here, these pads 4 including the input and output pads 41 to 43 and the test pad 40 are all arranged on the inside of the scribe line 3, that is, at the product region 2, respectively. Further, when the die sorting test is executed during the manufacturing process, some needles (e.g., probes) are brought into contact with these pads 4. Further, when the product test is executed, some voltages and some signals are inputted through the bonded pads of the semiconductor device, and some signals are outputted through an appropriate pad. As described above, in the case of the semiconductor wafer, the tests (i.e., the die sorting test, the product test, etc.) must be executed at least once, respectively as a rule. In particular, the ROM test at the product region 2 is executed in the same process as the other tests. Therefore, in case the test conditions of the semiconductor products manufactured after the scribe step and then put on the market are decoded or deciphered by some method or other, since the ROM test conditions can be known and realized by another person, it is possible to read the contents of the ROM of the semiconductor device. In particular, when the semiconductor device is used for the electronic transactions, in case the contents of the ROM are read and decoded (deciphered), there exists such a danger that the read contents are used improperly or illegally.
With the advance of the recent development of the semiconductor devices, it has become possible to execute the electronic transactions by use of these semiconductor devices (e.g., IC cards). When the electronic transactions are put to practical use in the field of electronic commerce, there exists such a large advantage that the transactions can be executed momentarily through a network. In order that the electronic transactions can be accepted from a social point of view, although there exists a large problem of how to construct its social system, in particular the development related to security technology for the semiconductor devices is the most important problem to be solved. Here, the important problems related to security in the internet system are four of "look furtively", "alter documents", "impersonate another person", and "pretend not to know". Here, "look furtively" implies that the important information is known by a third person in the network. In the electronic transactions, the card number data is known by another person and used illegally. "alter documents" implies that the important information is rewritten in the networks. In the case of the electronic transactions, when the value of money is designated so as to be transferred between the two accounts, the transferred account is rewritten. Or else, when the electronic money is remitted, an amount of money to be remitted is rewritten. "impersonate a person" implies to transmit information by impersonating another person, because the person's face cannot be seen in the network. In the electronic transactions, a consumer is deceived by a retail shop pretending a socially fine reputation, requested to remit electronic money, and thereby defrauded of the remitted electronic money. "pretend not to know" is to deny that electronic money is not yet received, in spite of the fact that the electronic money has been already remitted. In the electronic transactions, in spite of the fact that a commodity sent by a retail shop has been already received, a consumer pretends not to receive the commodity.
However, since these problems can be soon solved with the advance of the technical development, the relative importance of the problems related to the electronic transactions and the electronic money will be shifted to the social system. In addition, in order to construct the society where the electronic transactions and the electronic money can be both accepted socially, it is necessary to change the paradigm from "security" to "comfort" (See NIKKEI ELECTRONICS 1996, 12, 16 pp171-181).
Therefore, in order to secure the security of the electronic transactions and electronic money, it Is important to prevent the contents of the semiconductor device such as an IC or LSI from being known by another person. When the test conditions of the semiconductor device products already put on the market are decoded by some way or other and thereby the test conditions of the ROM can be realized by another person, since the contents of the ROM can be read, in the case of the semiconductor device used for electronic transactions, it has been necessary to eliminate such a danger that the contents of the ROM are decoded and used illegally.